Identification and evaluation of cold tolerance of 54 maize inbred lines and 16 hybrids at seedling stage

【Objective】The identification and evaluation of cold tolerance on maize inbred lines and hybrids in Guizhou as well as the screening of cold tolerant germplasm resources for alpine regions were conducted,which could provide references for early spring sowing and breeding of maize in Guizhou high-altitude and cold regions areas. 【Method】In this study,54 maize elite inbred lines and 16 hybrids in Guizhou were used, the 9 cold tolerance related indexes including days to emergence, days to the second leaf,early vigor,fresh weight above aground,dry matter weight above aground,relative chlorophyll content（SPAD）, initial fluorescence（F_o）, actual light energy conversion efficiency （ΦPSII）, maximum light energy conversion efficiency（F_v/F_m） were measured indoor low temperature treatment（14 ℃）, outdoor low temperatrue treatment（11.5 ℃） and control treatment（25 ℃） were set. Comprehensive membership function analysis and cluster analysis were applied to assess cold tolerance at the seedling stage of inbred lines and hybrids,aiming to screen and identify cold tolerant germplasm resources suitable for cultivation in high-altitude and cold regions regions. 【Result】Variance analysis revealed that 7 cold tolerance related indexes were significantly or highly significantly influenced by genotype and temperature treatment. Under cold stress indoor, days to the second leaf showed significantly negative correlation with early vigor and fresh weight above aground（P＜0.05, the same below）;early vigor was significantly and positively correlated with dry weight above ground and fresh weight above ground, F_o exhibited significant negative correlations with both ΦPSII and F_v/F_m. In control conditions, early vigor was significantly and negatively correlated with days to emergence, but significantly and positively correlated with fresh weight above ground, dry weight above ground and SPAD. The mean days to emergence and days to the second leaf of the inbred lines and hybrids treated in the control were both lower than those treated at indoor and outdoor low temperatures. The mean values of SPAD, ΦPSII, F_v/F_m and fresh（dry） weight above ground were higher than those treated at indoor and outdoor low temperatures. The mean value of F_o of the inbred lines treated in the control was lower than that at indoor and outdoor low temperatures, and that of the hybrids was lower than that at indoor low temperature, but higher than that at outdoor low temperature. Under the control treatment, the coefficients of variation of fresh weight above ground and dry weight above ground of the inbred lines and hybrids were larger than those of other indexes, while the coefficients of variation of ΦPSII and F_v/F_m were smaller. This indicated that under the control treatment, similar variation trends were presented in the inbred lines and hybrids. The broad-sense heritability of the dry weight above ground and F_v/F_m was relatively high under indoor low temperature treatment. The broad-sense heritability variation range of cold tolerance related indexes of inbred lines and hybrids under indoor and outdoor low temperature treatment was relatively large（0.01-0.95）, indicating that most cold tolerance related indexes were mainly affected by genetic factors and cold damage. Fifty-four inbred lines were classified into three major groups. The order of cold resistance was group Ⅱ ＞ group Ⅲ ＞ groupⅠ. The material with the highest membership value of group Ⅱ was GD932, which was 6.27. The materials with the highest membership values of group Ⅲ were Zhaoyu 001 and ES40, which were 6.1 and 5.95 respectively. It could be seen that the materials in group Ⅱ and group Ⅲ exhibited strong adaptability. Among the 16 hybrids, the membership values of Jinyu 932 and Qianyu No. 3 were relatively high, which were 7.87 and 5.62 respectively, and they had strong cold tolerance. The cold tolerant hybrid superior models of the two were Red×local germplasm and Red×Suwan. 【Conclusion】The top 4 materials in terms of total membership values, GD932, Zhaoyu 001, ES40 and Jinyu 932, are strong cold tolerant germplasms and can be used as parent materials for corn breeding in high-altitude and cold regions. The cold tolerance of tropical germplasm groups is higher than that of local background and Red groups. The hybrid superior model of Red background×local background should be focused on in cold tolerant breeding of maize and early spring sowing at high altitudes.